Single-step, high pressure, and two-step spark plasma sintering of UO2 nanopowders

Three different spark plasma sintering (SPS) treatments were applied to highly sinteractive, near-stoichiometric UO2.04 nanocrystalline (5 nm) powders produced by U(IV) oxalate hydrothermal decomposition at 170 °C. The conditions for reaching 95 % theoretical density (TD) in regular SPS, high pressure SPS (HP-SPS), and, the first time, two-step (2S-SPS), determined. Densification TD was achieved 1000 °C (70 MPa pressure), 660 HP-SPS (500 MPa), and 650−550 2S-SPS MPa). With goal of minimising grain growth during densification, optimised favour densification over coarsening, final microstructures thus obtained are compared. Equally dense UO2 samples sizes, ranging from 3.08 μm 163 nm, produced. Room-temperature oxidation could not be avoided due their nanometric dimensions, a annealing treatment designed reduce hyperstoichiometric UO2.00.